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Posted by: 930cabman Sep 3 2021, 01:16 PM

We are building a 2.1 /4 cyl. motor and have sent the rotating parts for balancing. Prior to I had the flywheel resurfaced at NAPA. Unknowing they removed the dowel pins that locate the pressure plate. I got all the parts to an old friend for balancing (he owed me a favor) and he turned the rotating parts around for me. He balanced the crank by itself, then added the fan and flywheel, but NOT the pressure plate.

Question: The factory book states the pressure plate should be aligned with the flywheel with the mating marks. The flywheel was not mounted to the flywheel due to the lack of dowel pins and is the pressure plate balanced by itself or as part of the assembly?

Posted by: johnhora Sep 3 2021, 03:34 PM

930cabman....

for full race engines we balance all the rotating mass we can...

for street if it's out balance it...but don't fret...

think about if a replacement clutch package is installed on a running car...disc/PP/flywheel machined....you just slap it in and go

Posted by: Mark Henry Sep 3 2021, 05:39 PM

Should have been done together, but get a KEP stage 1 pressure plate, last few jobs I've done with KEP PP's my balance guy said they were spot on.

Posted by: 930cabman Sep 3 2021, 05:51 PM

Yes, when the complete rotating assembly is spun up, there are no questions. I will look for a KEP unit. Thanks

Posted by: iankarr Sep 3 2021, 10:22 PM

My machinist needed to weld a washer to my Sachs pressure plate. Good to learn about KEP

Posted by: Mark Henry Sep 4 2021, 06:32 AM

If you want to wait I'll be taking another 914 stage one clutch to my balance guy and I can ask if it's in spec. But that may take 2-3 weeks till I get it back.

Posted by: 930cabman Sep 5 2021, 04:43 AM

I will be calling Kennedy Tuesday, see if they can confirm a 0 balance on their pressure plates.

Posted by: Superhawk996 Sep 5 2021, 07:45 AM

Nothing in life is zero balance. Even if someone tells you it's zero balance, there is still a tolerance to the equipment and process used to balance. Go measure same zero balance part on another machine and it's highly unlikely you'll get true zero.

Fully agree a fully dynamic balance of all rotating mass is ideal. Mandatory for high RPM race engines.

However, are you also having your fan dynamically balanced as part of the assembly? If not why not? Inclusive of fan hub and fasteners? Will all flywheel and pressure plate fasteners be placed back into exactly the same holes they were blanced in? You see where this is going.

As stated previously, for a road car, in normal production, components are balanced as individual parts. There is a print tolerance on each part and each part has a six sigma variance of what it could be in actual production. A Monte Carlo simulation can be used to understand what the final balance liklihood is of a given outcome. Most times, some parts will be a little on the plus side, some on the minus side. Same with respect to how they index. In the end, it all works out within an acceptable range due to the statistics and probability working against all parts being all on the plus side or all parts on the minus side simultaneously.

Not saying that you shouldn't dynamically balance. However, let's recognize that OEM was not built that way. Full dynamic balance is nice to do for a road car but not a necessity. My first rebuild wasn't dynmaically balanced, I had neither the money to do it nor access to a vendor that could do it back in the day. That engine ran about 100K miles, no issues.

Posted by: 930cabman Sep 5 2021, 01:31 PM

Back in the 1970's that was my full time job in the family business, and I got pretty good at it. My thought was, while the 2.0/4 is apart, why not. I still have a few friends in the business and dropped the rotating components off, but forgot to include new dowel pins for the PP. My local NAPA had resurfaced the flywheel and removed the dowel pins.

Posted by: rgalla9146 Sep 6 2021, 10:20 AM

At least they knew enough to machine the mounting surface too.